Technical Field
The present invention relates to a semiconductor device fabricating method and a semiconductor device.
Related Art
Metal-insulator-metal (MIM) capacitors are known as capacitor elements in semiconductor devices. FIGS. 7A to 7E are sectional views schematically showing a process by which a semiconductor device 90 including a MIM capacitor C pertaining to related art is fabricated (Japanese Patent Application Laid-open (JP-A) No. 2013-191764).
When forming the MIM capacitor C, as shown in FIG. 7A, an interlayer insulating film 301 is formed on a semiconductor substrate 300. Thereafter, a Ti/TiN/Al/Ti film (a multilayer film comprising a titanium (Ti) film 302a, a titanium nitride (TiN) film 302b, an aluminum (Al) film 302c, and a titanium (Ti) film 302d that have been sequentially layered on top of one another from the bottom) that is a lower electrode 302 is formed using sputtering, for example.
Next, a silicon oxynitride (SiON) film that is an insulating film 303 is formed on the lower electrode 302 using chemical vapor deposition (CVD). The insulating film 303 configures a capacitor insulating film in the MIM capacitor C, and the film thickness of the insulating film 303 is set in accordance with, for example, the capacitance of the MIM capacitor C. Next, as shown in FIG. 7B, a TiN film serving as an upper electrode 304 is formed on the insulating film 303 using sputtering.
Next, as shown in FIG. 7C, patterning of the upper electrode 304 is performed using lithography and dry etching. In this patterning, the section of the upper electrode 304 outside the region in which the MIM capacitor C is to be formed (a MIM capacitor formation region 330) is removed, but because the insulating film 303 is left, the lower electrode 302 is not etched.
Here, if the insulating film 303 is not left and the lower electrode 302 is exposed, reaction products that occur during the dry etching stick to the side wall section of the MIM capacitor formation region 303 and lead to a poor breakdown voltage. For that reason, it is preferred that the insulating film 303 be left.
Next, as shown in FIG. 7D, an insulating film 305 that becomes part of an antireflection film in a lithography step when processing the lower electrode 302 described below is formed on the total surface of the insulating film 303. In this related art, a SiON film, which is to say the same type of film as the insulating film 303, is used as the insulating film 305. Consequently, in the region outside the MIM capacitor formation region 330, the insulating film has a multilayer structure comprising the insulating film 303 and the insulating film 305.
Next, as shown in FIG. 7D, the lower electrode 302 is patterned using lithography and dry etching. The multilayer structure, comprising the SiON film serving as the insulating film 305 and the SiON film serving as the insulating film 303, acts as an antireflection film in an exposure step in this lithography.
Next, as shown in FIG. 7E, an interlayer insulating film 306 (in this related art, a silicon oxide (SiO2) film) is formed, and thereafter vias 322, plugs 307 that plug the vias 322, and upper wires 308 that are electrically connected to the plugs 307 are formed.
Through the above process, the MIM capacitor C, which has a structure wherein the insulating film 303 (SiON film) that is the capacitor insulating film is sandwiched between the lower electrode 302 and the upper electrode 304 that are two electrodes, is formed.
In the semiconductor device fabricating process disclosed in JP-A No. 2013-191764, the insulating film 303 that is the capacitor insulating film and the insulating film 305 that is the antireflection film are each formed by a SiON film.
The relative permittivity of a SiON film is relatively low, and when a SiON film is used as the insulating film 303 that is the capacitor insulating film, it is necessary to make the film thickness of the SiON film thinner in order to increase the capacitance of the MIM capacitor C. However, when the insulating film 303 is made thinner, it becomes easier for the problem of a poor breakdown voltage to occur.
At the same time, the reflectance of the SiON film used as the insulating film 305 that is the antireflection film is highly dependent on film thickness, and is necessary to manage the film thickness to a predetermined value. Moreover, as mentioned above, in the region outside the MIM capacitor formation region 330, the antireflection film has a multilayer structure comprising the insulating film 305 and the insulating film 303, so it becomes necessary to consider both capacitance and reflectance, and managing the film thickness becomes even more difficult.
As described above, in the related art using SiON films as the insulating film of the capacitor insulating film and the insulating film of the antireflection film, there is a tradeoff between the capacitance of the MIM capacitor C and the breakdown voltage, so it becomes difficult to satisfy both functions, and furthermore managing the film thickness of both insulating films also becomes difficult.
On the other hand, if a SiN (silicon nitride) film, which has a higher relative permittivity than a SiON film, is used as the capacitor insulating film from the standpoint of increasing the capacitance of the MIM capacitor C, it becomes easier to achieve a balance between the capacitance of the MIM capacitor C and the breakdown voltage.
However, in this case it becomes necessary to form on the SiN film a separate SiON film to serve as an antireflection film because the SiN film transmits the light used in the exposure step. For that reason, the antireflection film comes to have a two-layer structure comprising the SiN film and the SiON film layered thereon, the film that must be patterned increases, and its function as an antireflection film drops, so the patterning of the lower electrode 302 ends up becoming difficult.